Information from sensory inputs converges in the thalamus before passing on to the cerebral cortex. The thalamus plays an important role in the processing and gating of this information. For example, the nature of the information that the thalamus relays to the cortex differs depending on whether one is awake or asleep. Thus the thalamus must be capable of rapidly modulating sensory information on a time scale of milliseconds. Many mechanisms are thought to contribute to this dynamic process, ranging from changes that occur at the molecular level to interactions of neurons at the network level. This proposal addresses the hypothesis that mechanisms of synaptic plasticity contribute significantly to the processing of incoming sensory information in the thalamus. To test this hypothesis, we will examine the connection between the retina and visual thalamus, the retinogeniculate synapse. The visual system is one of the best-studied systems for information processing, and the incoming visual information, encoded in the firing patterns of retinal ganglion cells, has been well characterized. Little, however, is known of the synaptic processes important in relaying this information from the retinal ganglion cells to thalamocortical neurons of the dorsal lateral geniculate nucleus (dLGN). In order to identify mechanisms important to the relay of information at the retinogeniculate synapse, a combination of electrophysiological and optical techniques will be used. Both the characteristics of the presynaptic retinal input and the response of postsynaptic thalamic relay neurons will be monitored. Mechanisms that underlie short-term synaptic plasticity will be identified and characterized by examining the synaptic response to pairs of retinal fiber stimuli and stimulation patterns that mimic retinal ganglion cell activity. In addition, the modulation of the retinogeniculate synapse by neurotransmitter projections from brainstem inputs and intrinsic inhibitory connection will be evaluated. Finally, the effects of these synaptic mechanisms of plasticity will be examined on the firing patterns of postsynaptic thalamic relay neurons. These studies will enhance our understanding of the contributions of synaptic mechanisms to information processing in the central nervous system. [unreadable] [unreadable]